Optical systems can be adapted to perform many functions. As elements within those optical systems, beam processing elements are useful for many applications, e.g. spectroscopy, telecommunications and interferometry. In these applications, it is often desired to employ a beam processing element to split a source beam into two or more output beams or to combine two or more optical beams into a single beam. Such elements may operate independently or in the context of an array of optical input/output ports where beams are split, combined, multiplexed, demultiplexed, added, dropped and/or otherwise processed.
The case of a beam splitter is illustrative. A beam splitter functions to separate an input beam into two or more output beams. One example of a beam splitter application is spectrographic analysis where one beam illuminates a reference sample and another beam illuminates a sample under analysis. It is desirable to generate these beams from a common source so as to simplify design and minimize artifact due to optical system differences. Accordingly, such systems may be implemented using a single source with a beamsplitter to provide the reference and sample path output beams.
There are a number of potential considerations for beamsplitter design in such contexts. For example, one consideration is efficiency or maximizing transmission of light from one part of a system to another part of the system by, for example, minimizing loss of light (visible or non-visible spectrum) due to transmission onto spurious or non-useful paths. Efficiency concerns in optical systems can be addressed at the level of each element as well as the overall system design. Efficiency is important for a number of reasons, including minimizing the required source power, limiting the need for repeaters in systems and maximizing the power of the output beams. In the application of spectroscopy, the efficiency of the beamsplitting function can affect the accuracy of measurements made of the sample and the reference, the power or range of the system for a given source, and the limits of the system's overall accuracy.
Another important consideration is noise in the optical system due to the beamsplitting function. Noise can be any type of extraneous or undesired signal component or characteristic. For instance, noise associated with the light in the system can affect its phase, its wavefront, its intensity, its polarization or any other of its characteristics. Such noise can adversely impact system performance and the accuracy of measurements, which may be of critical importance for certain applications. In the application of spectroscopy, the noise created by the beamsplitting function can, among other things, affect the accuracy of the measurements made by the system by creating differences between the sample and reference path beams that are not a function of sample or reference fluid composition. Noise can entail, for example, plane parallel cavity beam shape artifact due to certain beamsplitter designs.
Another important consideration in beamsplitter design is the accuracy with which the spatial relationship of the output beams can be controlled. Accuracy relates to, for example, controlling the spacing and other relative geometry of the output beams. Also, accuracy can encompass, for example, controlling the size, shape, intensity and other characteristics of the output beams. For example, in spectroscopy applications involving analysis of a fluid such as atmospheric gases, accurate control of the intensity and positioning of the output beams is crucial. The importance of different types of accuracy within an optical system will vary with the function of the optical system.
Other potential considerations relating to beam splitter design include the difficulty and expense of manufacturing and limiting differences in the optical pathways/elements of the beams. In the last regard, optical systems can benefit from the use of monolithic components. Systems involving multiple optical elements or otherwise non-monolithic components can entail concerns relating to, for example manufacturing precision, thermal drift of characteristics of the components and path specific artifact.